The present invention relates in general to vortex shedding flowmeters and in particular to a new and useful circuit arrangement for vortex shedding flowmeter sensors utilizing digital techniques for processing the flowmeter signal.
It is known that when a non-streamlined obstacle is presented in a fluid flow path that vortices are shed from alternate sides of the obstacle. The obstacle is termed a bluff body and utilized as a vortex shedding flowmeter with sensing means for sensing the passage of the vortices. The frequency of passage of the vortices is directly proportional to the volumetric flow in the flow path.
It is known to amplify the signal from the vortex sensor and to use various structures for the sensor itself.
It is known that the signal for the vortex sensor has fluctuating amplitudes due to non-uniformities in the flow being measured. This gives noisy or fluctuating signals at the output of a flow transmitter using a vortex shedding sensor in many applications. This is observed as an intermittent loss of signal.
Examples of vortex shedding flowmeters and their connecting circuitry can be found in U.S. Pat. No. 4,134,297 to Herzel; U.S. Pat. No. 4,123,940 to Herzl et al.; and U.S. Pat. No. 4,033,188 to Herzl.
One of the units which is utilized in the combination and method of the present invention is the so-called UART unit or Universal Asynchronous Receiver Transmitter. These units are examplified by CMOS-LSI-UART units such as IM-6402 and IM-6403. The receiver section of such units converts serial data into parallel data and the transmitter converts parallel data into serial data. The UARTs can thus be utilized to interface with computers or microprocessors.
Phase-Locked Loop Units, as exemplified by RCA-CD4046B, COS-MOS phase-lock loops include a voltage controlled oscillator which tracks an input frequency and, if the input frequency disappears, maintains the last frequency value. Such a Phase-Lock Loop uses low power and incorporates a low pass filter which produces an analog voltage signal which corresponds to the frequency of the frequency signal being tracked.